I. Field of the Invention
The present invention generally relates to mobile telephones and in particular to the audio microphone and speaker of a mobile telephone.
II. Background
Cellular telephones and other mobile telephones are commonly employed within a wide range of differing noise environments. For example, a cellular telephone may be employed within a relatively quiet office or home environment or within a relatively noisy manufacturing or traffic environment.
In a noisy environment, a user tends to speak more loudly into the microphone of the cellular telephone than in relatively quiet environments. This is a natural tendency arising from the assumption by the user that he or she must speak more loudly to be heard over the noise. Yet such is often not necessary and, indeed, may be counterproductive. The microphone of the cellular telephone may be highly directional and therefore will not detect and amplify all of the noise that the user hears. Hence, it is unnecessary for the user to speak more loudly. Moreover, the cellular telephone may be capable of processing only a limited dynamic range of sound levels such that the voice of the user becomes clipped if the user speaks too loudly into the microphone. Such clipping can result in a decrease in the signal-to-noise ratio (SNR) between the transmitted voice and the transmitted background noise level. Hence, speaking loudly into the microphone may actually make it more difficult for the listener to distinguish the voice of the user.
The clipping phenomenon described above is illustrated in FIGS. 1-2. More specifically, FIG. 1 illustrates a voice signal 10 and a background noise signal 12 input to a cellular telephone. The background noise level increases beginning at time 14. In response thereto, the user speaks more loudly, resulting in an increase in the input voice signal level. As the noise level continues to rise, the user speaks even more loudly until reaching a point 16 where clipping begins. Thereafter, the voice is clipped, yielding a lower SNR as well as a possibly distorted voice signal. FIG. 2 illustrates the resulting changes in the SNR. As can be seen, the SNR decreases following time 16.
Hence, in circumstances where clipping occurs, a user who tries to speak more loudly can actually reduce intelligibility. Even if clipping does not occur, the user speaking more loudly may cause annoyance to the listener, perhaps resulting in a need for the listener to decrease the volume of the speaker of his or her telephone. For many telephones, particularly non-mobile telephones, the volume of the speaker cannot be adjusted and hence the listener may not be able to achieve a comfortable volume level. Moreover, privacy may be jeopardized at the listener""s end if the voice of the user is too loud and the listener cannot decrease the speaker volume level.
Another problem arising from high noise levels is that it may be difficult for the user in the noisy environment to hear the voice of the other party. For many cellular telephones, the volume or gain of the speaker of the telephone can be manually increased to compensate, but such manual action by the user is inconvenient. Moreover, manual action may be dangerous, particularly if the user is driving in traffic while attempting to manually decrease the speaker gain.
Additionally, some users speak relatively softly, while other users speak relatively loudly. It is inherently difficult to design microphone gains to provide adequate gain for soft talkers without saturating loud talkers.
Accordingly, there is a need to remedy the foregoing problems, and it is to that end that the invention is primarily drawn.
The foregoing problems are addressed by providing a cellular telephone, or other mobile telephone, with a means for adjusting the gain of a microphone of the telephone based upon the detected noise level in which the cellular telephone is operated. As the noise level increases, the gain of the microphone is automatically decreased, thereby compensating for the tendency of telephone users to speak more loudly in noisy environments. Also, by decreasing the microphone gain, any clipping that might otherwise occur as a result of the user speaking more loudly is avoided and the SNR is thereby not decreased. Furthermore, because the microphone gain decreases, the volume level of the voice of the user as it is output from the telephone of the other party to the telephone call is not unduly loud. Hence, the other party need not manually decrease the speaker gain of his or her telephone.
In an exemplary embodiment, automatic microphone gain adjustment is achieved by providing the cellular telephone with a means for detecting the background noise level of the environment in which the mobile telephone is operating and a means for setting the gain of a microphone of the mobile telephone based upon the detected background noise levels. The means for setting the gain of the microphone operates to decrease the gain in response to an increase in background noise by an amount inversely proportional to the background noise level. In the exemplary embodiment, the microphone gain is reduced by half the value of the increase in background noise measured in decibels.
In the exemplary embodiment, the mobile telephone further includes a means for automatically setting the gain of a speaker of the mobiles telephone based upon the background noise level. More specifically, the means for setting the gain of the speaker operates to increase the gain in response to an increase in the background noise level. Hence, the user need not manually increase the speaker gain if the background noise level increases.
The invention is particularly well suited for use in cellular telephones employing digital signal processing (DSP) units. Many such cellular telephones include hardware or software within the DSP for calculating the background noise level from the input signal for the purposes of performing noise reduction. An exemplary embodiment for calculating the background noise level is described in detail in U.S. Pat. No. 5,414,796, entitled xe2x80x9cVariable Rate Vocoder,xe2x80x9d which is assigned to the assignee of the present invention and incorporated by reference herein. With such cellular telephones, the DSP is merely reconfigured or reprogrammed to apply the detected noise level to look-up tables relating various noise levels to appropriate speaker and microphone gain levels. A wide variety of other implementations are also possible.
In one aspect of the invention, a device for adjusting gain in a microphone of a communications device advantageously includes adjustable digital gain logic coupled to the microphone; and a limiter coupled to the adjustable digital gain logic, the limiter being configured to perform peak detection on a speech signal that is input to the microphone.
In another aspect of the invention, a method of adjusting gain in a microphone of a communications device advantageously includes the steps of applying a digital gain to a signal that is input into the microphone; and limiting the digital gain.
In another aspect of the invention, a device for adjusting gain in a microphone of a communications device advantageously includes means for applying a digital gain to a signal that is input into the microphone; and means for limiting the digital gain, the means for limiting being configured to perform peak detection on the signal.
Thus, with the invention, the above-described problems occurring when cellular telephones or other mobile telephones are used in environments having high background noise levels are substantially overcome. An advantage of the present invention is that the need for a volume control button on a telephone is eliminated. Other advantages of the invention, as well as other features and objects of the invention, will be apparent from the detailed description which follows and from the accompanying drawings.